Bipolar radio frequency ablation device with retractable insulator and method of using same

ABSTRACT

An ablation device, comprises a first tubular element and a first electrode which, when in an insertion configuration, is received within the first tubular element, the first electrode being deployable from the first tubular element to anchor in a target portion of tissue at a first electrode operative position in combination with a second electrode which, when in the insertion configuration, is received within the first tubular element, the second electrode being deployable from the first tubular element to anchor in the target portion of tissue at a second electrode operative position separated from the first electrode operative position, the second electrode being deployable independently of the first electrode and an insulating element movable relative to the first electrode to insulate selected portions of the first electrode. A method of ablating tissue, comprises anchoring a first electrode at a first location in a target portion of tissue, deploying a second electrode at a second location in the target portion of tissue and applying current between the first and second electrodes to ablate a first ablation portion of tissue between the first and second electrodes in combination with moving an insulative cover relative to the first electrode to move a conductive portion of the first electrode to a third location within the target tissue, the third location being further from the second location than the first location, moving the second electrode to a fourth location within the target tissue, the fourth location being further from the first location than the second location and applying current between the conductive portion of the first electrode and the second electrode to ablate a second ablation portion of tissue surrounding the first ablation portion of tissue.

BACKGROUND

Ablation is often recommended for the treatment for fibroids tumors andother tissue masses. Local ablation may be carried out by inserting atherapeutic device into target tissue and performing a therapeuticactivity to destroy targeted cells. For example, electrical energy maybe applied to the target tissue by discharging electric current from oneor more electrodes placed in the target tissue. Alternatively, fluidswith appropriate properties may be injected into the vicinity of thetarget tissue to chemically necrose the tissue.

Target tissues such as tumors and fibroids are often not securelyanchored in place within the body, but instead are loosely joined to thesurrounding tissue by ligaments and other structures. Accordingly, itmay be difficult for a surgeon to insert a needle electrode or otherenergy delivery devices into the target tissue as the tissue may move asthe surgeon attempts to puncture it with such a device. Grasping devicesand anchors may be used to immobilize the tissue while an electrode isinserted thereinto, but this increases the complexity of the operationand may require additional incisions and/or assistance from additionalpersonnel.

The size of the apparatus used to perform such procedures is minimizedto reduce trauma to the patient. However, the small size of the ablationprobe decreases the size of the ablation area. Because of the reducedsize of the ablation region, it may be necessary to perform ablations oflarger tissue masses in multiple stages at different locations beforethe entire volume of target tissue is ablated. In addition, thedifficulty in inserting electrodes into many types of target tissuescomplicates the procedure and increases the time required for and thetrauma associated with the procedure.

SUMMARY OF THE INVENTION

In one aspect, the present invention is directed to an ablation device,comprising a first tubular element and a first electrode which, when inan insertion configuration, is received within the first tubularelement, the first electrode being deployable from the first tubularelement to anchor in a target portion of tissue at a first electrodeoperative position in combination with a second electrode which, when inthe insertion configuration, is received within the first tubularelement, the second electrode being deployable from the first tubularelement to anchor in the target portion of tissue at a second electrodeoperative position separated from the first electrode operativeposition, the second electrode being deployable independently of thefirst electrode and an insulating element movable relative to the firstelectrode to insulate selected portions of the first electrode.

The present invention is further directed to a method of ablatingtissue, comprising anchoring a first electrode at a first location in atarget portion of tissue, deploying a second electrode at a secondlocation in the target portion of tissue and applying current betweenthe first and second electrodes to ablate a first ablation portion oftissue between the first and second electrodes in combination withmoving an insulative cover relative to the first electrode to move aconductive portion of the first electrode to a third location within thetarget tissue, the third location being further from the second locationthan the first location, moving the second electrode to a fourthlocation within the target tissue, the fourth location being furtherfrom the first location than the second location and applying currentbetween the conductive portion of the first electrode and the secondelectrode to ablate a second ablation portion of tissue surrounding thefirst ablation portion of tissue.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view showing the RF ablation device according toan embodiment of the invention in a first configuration; and

FIG. 2 is a schematic view showing the RF ablation device of FIG. 1 in asecond configuration.

DETAILED DESCRIPTION

The present invention may be further understood with reference to thefollowing description and the appended drawings, wherein like elementsare referred to with the same reference numerals. The present inventionis related to medical devices used to destroy tissue less invasively. Inparticular, the present invention relates to devices for ablating tissuesuch as fibroids, tumors and other masses using electric energy providedthrough a needle-like device which is inserted into target tissue.

In one embodiment, the elements used to deliver therapeutic energy (suchas electrical current) to the target tissue as well as the devices usedto grasp and hold target tissue in place are both deployable from asingle medical instrument. Thus, the number of incisions or puncturesnecessary to perform the medical procedure is minimized and theprocedure can be carried out with a reduced number of personnel.Embodiments of the invention provide for a dual electrode device whoseeffective ablation volume may be changed while the device is inserted inthe target tissue, without having to remove the device and re-insert itinto the target tissue.

Conventional systems for ablating tissue with needle-based devicesinclude, for example, the LeVeen Needle Electrode™ from the OncologyDivision of Boston Scientific Corp. and the Starburst™ product lineavailable from RITA Medical Systems, Inc. When using these devices, thesurgeon punctures the target tumor with the device's needle and thendeploys one or more radio frequency (RF) tines into the tissue mass. Anelectric voltage is then applied to the tines to ablate the targettissue.

It may be difficult to use these devices with many tumors or fibroids asthese tissue masses may move as the surgeon attempts to insert theneedle thereinto. As described above, the tissue masses are often onlyloosely held to the surrounding tissue by ligaments or connectivetissues possibly requiring multiple attempts before the needle ispositioned correctly. Alternatively, a grasping device such as a tumorscrew may be used to immobilize and apply traction to the target tissuewhile the needle is inserted. This approach simplifies insertion of theneedle into the tissue mass, but increases the complexity of the overallprocedure, especially if multiple entry points through the skin are usedto position the grasping device and the needle. Moreover, theseprocedures require the surgeon to manipulate several devicessimultaneously, and may require the assistance of other personnel tocomplete the operation.

Many conventional RF tissue ablation devices are monopolar (i.e.,electrodes of only one polarity are inserted into the target tissue withan exterior grounding pad drawing current from the electrodes, throughthe target tissue). Such monopolar RF ablation devices may cause damageto non-targeted tissue between the electrodes and the grounding padsincluding burns to the skin contacted by the grounding pad. In order toachieve desired ablation levels, monopolar delivery systems may requireenergy delivery times and power levels increased relative to thoseassociated with bi-polar systems. However, monopolar RF ablation devicesare used extensively because they operate with only a single electrodeinserted per incision.

One embodiment of a tissue ablation system according to the presentinvention combines an array of radio frequency (RF) tines with ananchoring coil to form a device for the therapeutic treatment of targettissue masses including fibroids and tumors. In one exemplaryembodiment, the anchoring coil used to stabilize the target tissue andto facilitate insertion of the needle also serves as one of the poles ofa bipolar RF system with the tines forming the other pole of the bipolarsystem. This design offers the advantages of stabilization of the targettissue during insertion of the needle and deployment of the tines, aswell as the increased efficiency and other benefits of delivering the RFenergy through a bipolar electrode arrangement. Additional groundingpads are not required when using the system according to the invention,and the electrical energy delivery time is considerably shortened ascompared to procedures using monopolar systems.

The tissue ablation system according to the invention also causes alarger lesion in the target tissue, by following a staged energydelivery approach in which the target tissue is ablated in two or morephases. As will be described in greater detail below, a first region isablated while the two electrodes are in an initial position and acurrent flows therebetween. The location of the electrodes is thenchanged, without removing the device from the target tissue, and theapplication of current is repeated to ablate a second region of thetarget tissue. The process may be repeated additional times, dependingon the specific configuration of the electrodes and on the size of thetarget tissue being treated.

In one exemplary embodiment, the location of a first electrode is variedwithin the target tissue by pushing the first electrode into the targettissue and by extending or withdrawing a movable insulating sleeveplaced over the first electrode. For example, the insulating sleeve maybe adapted to extend into the target tissue mass over an anchoring coilwhich serves as the first electrode. The insulating sleeve may beextended or retracted relative to the longitudinal length of the firstelectrode, to vary the size of a portion of the first electrode ineffective contact with the target tissue mass.

In the context of this application, the portion of the first electrodein effective contact with the target tissue mass (area of effectivecontact) refers to an area surrounding a portion of the first electrodenot covered by the insulating sleeve or by an insulating tubular elementand which is in contact with target tissue that has yet to be ablated.In contrast, the portion of the first electrode within such aninsulating sleeve or tubular element or which is in contact with targettissue which has already been ablated is not part of the area ofeffective contact as tissue which has already been ablated is not aneffective conductor of electricity and behaves similarly to aninsulating layer surrounding the electrode.

In an exemplary procedure for use of the device according to theinvention, a distal region of the first electrode is extended from adistal end of an insulating sleeve or tubular element and inserted intoa target tissue mass. The position of the insulating sleeve relative tothe first electrode is then adjusted so that only a selected distalregion of the first electrode is uncovered. The second electrode is alsodeployed in the target tissue mass so that a first portion 120 of thetarget tissue mass may be ablated in an initial ablation phase.

After completion of the initial ablation phase, the insulating sleevemay be withdrawn, to expose a more proximal region of the firstelectrode. As the initial ablation phase has ablated the tissuesurrounding the distal end of the first electrode, this is no longerpart of the area of effective contact. The area of effective contact nowincludes the area surrounding the newly exposed, more proximal region ofthe first electrode. Also, the second electrode may be pushed furtherinto the target tissue mass and re-deployed distally, outside of theportion of tissue ablated in the initial phase. The new locations of theeffective contact areas of the first and second electrodes and the pathsalong which the current will pass between them define a second portionof the target tissue mass to be ablated with the second portion radiallysurrounding the first portion 120.

Once the first and second electrodes have been re-deployed to their newpositions, a subsequent ablation phase is carried out. In the subsequentablation phase, the second portion of the target tissue mass is ablatedby applying a current between the effective contact areas of the firstand second electrodes. As the conductivity of the ablated first portion120 is greatly decreased, the current flows around the first portion 120through a second portion of the target tissue mass surrounding the firstportion 120, radially outward from it and forming a shell therearound.

FIG. 1 shows an exemplary embodiment of a bipolar RF ablation device 100with a retractable insulating element according to an embodiment of theinvention. FIG. 1 shows the configuration of the electrodes within atarget tissue mass 112 during the initial ablation phase while FIG. 2shows the configuration of the electrodes in a subsequent ablationphase. The device may include an insertion element such as first tubularelement 102, which is used to guide the RF ablation device along aworking lumen of an endoscope to a location adjacent to the targettissue 112. Alternatively, the first tubular element 102 may be aneedle-like cannula used to pierce biological tissues, so that itsdistal end may be placed in proximity to the target tissue mass 112.Tubular element 102 can also be inserted into the patient via a trocar.

A first electrode 104 may extend from a lumen of the first tubularelement 102, at the distal end thereof. The first electrode 104 ispreferably shaped like a coil or a corkscrew and rotatably mountedwithin the tubular element 102 to allow it to be screwed into the targettissue mass 112. Alternatively, first electrode 104 can be fixeddirectly to the cannula 102, allowing them to be rotated together. Adistal end 114 of the first electrode 104 is preferably formed as asharpened tip to facilitate tissue penetration and the size and pitch ofthe coils of the first electrode 102 are selected to provide sufficienttraction and gripping of the target tissue mass 112, without being solarge as to cause unnecessary trauma to the patient during insertion.The first electrode 104 may also be biased to expand to a largerdiameter after exiting the tubular element 102, to increase the grip onthe target tissue mass 112 while maintaining a smaller profile duringinsertion and withdrawal of the device 100. The first electrode 104 isreceived within the tubular element 102 so that it may be rotated andtranslated longitudinally relative thereto. A proximal handle or similaroperating device (not shown) may be provided to, facilitate rotation andtranslation of the first electrode 104 relative to the tubular element102.

An insulating sleeve 110 is received around the first electrode 104 andis slidable thereover to cover or uncover portions of the firstelectrode 104. The insulating sleeve 110 may preferably be formed as atube following the coil-like shape of the first electrode 104. However,the insulating sleeve 110 may also be formed as a slidable shellsurrounding encompassing an entire diameter of first electrode 104without contacting an inner diameter thereof. As would be understood bythose skilled in the art, various additional configurations of theinsulating sleeve 110 may be employed so long as the sleeve and theelectrode 104 are movable relative to one another to selectively exposeand insulate portions of the first electrode 104. The insulating sleeve110 may be formed of any suitable bio-compatible, electricallyinsulative material, such as polyimide, polyamide, teflon or otherfluoropolymers.

The device 100 further includes, at a distal end thereof, a secondelectrode 108. An insertion element, shown in FIGS. 1 and 2 as a needletubular element 106, may be used to contain a second electrode 108 priorto its deployment. The needle tubular element 106 is preferablysubstantially coaxial with the first electrode 104 and contained withinthe coils thereof. Thus, the first and second electrodes 104, 108 andthe needle tubular element 106 are contained within a central lumen ofthe first tubular element 102 during insertion of the device 100 intothe patient so that a profile of the device 100 is limited to an outerdiameter of the tubular element 102. After the first electrode 104 hasbeen anchored in the target tissue mass 112 as described above, theneedle tubular element 106 is extended from the distal end of thetubular element 102 through the coil of the first electrode 104 into thetarget tissue mass 112. The second electrode 108 is then deployed fromthe needle tubular element 106 at a position separated from the distalend of the first electrode by a distance selected to control a size andshape of the first portion 120, as shown in FIG. 1. The second electrode108 preferably comprises an array of tines 109, or a similar arrangementof multiple conductors. However, those skilled in the art willunderstand that, if desired, the second electrode 108 may be formed as asingle conductive element. Second electrode 108 may also be formed as aneedle or rod with one or more ring electrodes mounted to it. These ringelectrodes may be activated independently of one another. Both the firsttubular element 102, the needle tubular element 106 and the first andsecond electrodes 104, 108 may be formed, for example, of stainlesssteel, Nitinol, or other surgical metals as would be understood by thoseskilled in the art.

As described above, in the initial ablation phase depicted in FIG. 1,the first and second electrodes 104, 108 define a first portion 120 ofthe target tissue mass 112 which is to be ablated initially. For optimumperformance, the effective contact areas of the first and secondelectrodes 104, 108, respectively, are substantially equal. In thiscase, the deployed length of the first electrode 104 and the position ofthe insulating sleeve 110 are selected so that an area of the firstelectrode 104 along the length l, is substantially equal to alongitudinal extent of the second electrode 108. An electric potentialis applied to the first and second electrodes 104, 108, respectively, topass a current through the first portion 120 of the target tissue mass112 to necrose this tissue.

After completion of the initial ablation phase, the first and secondelectrodes 104, 108, respectively, are re-deployed as shown in FIG. 2with the second tubular element 106 pushed further into the targettissue mass 112 so that its distal tip is outside the first portion 120.The insulating sleeve 110 is then withdrawn proximally into the firsttubular element 102, to expose a more proximal portion of the firstelectrode 104 to the tissue therearound leaving the distal portion ofthe first electrode 104 anchored within the ablated tissue of the firstportion 120. As described above, due to the change in the conductivityof the first portion 120, only that part of the first electrode 104shown by the length l₂ is now in effective electrical contact with thesurrounding tissue. Therefore the insulating sleeve 110 is preferablyposition so that the effective tissue contact area of the firstelectrode 104 is substantially equal to the effective tissue contactarea of the tines 109 of the second electrode 108.

After the first and second electrodes 104, 108 and the insulating sleeve110 have been positioned as desired as shown in FIG. 2, a voltage isapplied therebetween to cause current to flow around the non-conductingablated tissue of the first portion 120 to ablate the second portion122. This procedure may then be repeated to ablate additionalsurrounding portions of tissue until the entire volume of the targettissue mass 112 has been ablated. This multi-step procedure allowslarger volumes of tissue to be ablated without removing and reinsertingthe ablation device 100.

An exemplary procedure to ablate a uterine fibroid is now described.During this procedure, the first tubular element 102 is inserted intothe abdomen of a patient percutaneously or through a trocar until thedistal end of the first tubular element 102 is positioned against thefibroid. The coil of the first electrode 104 is then extended from thedistal end of the tubular element 102 to insert the tissue penetratingdistal tip 114 thereof into the target tissue mass 112. The firstelectrode 104 is then rotated to screw the first electrode 104 into themass of the fibroid (i.e., the target tissue mass 112) to anchor thefirst electrode 104 therein. The needle tubular element 106 is theninserted into the target tissue mass 112, until its distal tip extendsat or beyond the first electrode 104. Once in position, the array oftines 109 is deployed from the tip of the needle tubular element 106 andelectrical energy is applied between the first and second electrodes104, 108 to ablate the first portion 120.

In the second step, the array of tines 109 is withdrawn into the secondtubular element 106, which is then pushed a further distance into thefibroid tissue 112, further away from the first electrode 104. The array109 is then re-deployed outside of the first ablation portion 120. Theinsulating sleeve 110 is withdrawn into the first tubular element 102 toexpose a non-insulated length of the first electrode 104 which isoutside of the first ablation portion 120. The current is thenre-applied between the two electrodes, to form a second ablation portion122.

The present invention has been described with reference to specificexemplary embodiments. Those skilled in the art will understand thatchanges may be made in details, particularly in matters of shape, size,material and arrangement of parts. For example, although the inventionwas described in the context of the treatment of uterine fibroids, othertumors may also be treated. Accordingly, various modifications andchanges may be made to the embodiments. Additional or fewer componentsmay be used, depending on the condition that is being treated using thedescribed anchoring and RF ablation devices. The specifications anddrawings are, therefore, to be regarded in an illustrative rather than arestrictive sense.

1-20. (canceled)
 21. A method of ablating tissue, comprising: anchoringa first electrode at a first location in a target portion of tissue;deploying a second electrode at a second location in the target portionof tissue; applying current between the first and second electrodes toablate a first ablation portion of tissue between the first and secondelectrodes; moving an insulative cover relative to the first electrodeto move a conductive portion of the first electrode to a third locationwithin the target tissue, the third location being further from thesecond location than the first location; moving the second electrode toa fourth location within the target tissue, the fourth location beingfurther from the first location than the second location; and applyingcurrent between the conductive portion of the first electrode and thesecond electrode to ablate a second ablation portion of tissuesurrounding the first ablation portion of tissue.
 22. The methodaccording to claim 21, further comprising inserting the first tubularelement to a deployment location while maintaining the first and secondelectrodes therewithin with the second electrode received within asecond tubular element within the first tubular element, wherein thesecond tubular element is inserted into the target tissue to the secondlocation for deployment of the second electrode therefrom.
 23. Themethod according to claim 21, wherein withdrawing, before moving thesecond electrode to the fourth location, the second electrode into thesecond tubular element and moving the second tubular element to thefourth location and re-deploying the second electrode therefrom.
 24. Themethod according to claim 23, further comprising—moving the conductiveportion of the first electrode by proximally translating the insulatingsleeve relative to the first electrode away from the first location. 25.The method according to claim 24, wherein the insulating sleeve isretracted until the effective tissue contact area of the conductiveportion of the first electrode along an axis of the first cannula issubstantially equal to the effective tissue contact area of the secondelectrode along the axis.
 26. The method according to claim 21, furthercomprising repeating the steps of the method to ablate successivelylarger tissue masses.
 27. A method of ablating tissue, comprising:inserting a tubular element having a lumen into tissue; advancing acoil-shaped electrode distally from the tubular element to a firstlocation in a target portion of tissue; advancing a second electrodecoaxially contained within the coil-shaped electrode to a secondlocation in the target portion of tissue, the second location beingdistal to the first location; applying current between the coil-shapedand second electrodes to ablate a first ablation portion of tissue;retracting an insulative cover proximally relative to the coil-shapedelectrode; advancing the second electrode distally to a third locationwithin the target tissue; and applying current between the coil-shapedand second electrodes to ablate a second ablation portion of tissue. 28.The method of claim 27, wherein advancing the coil-shaped electrodedistally comprises rotating the coil-shaped electrode.
 29. The method ofclaim 27, wherein the second ablation portion radially surrounds thefirst ablation portion.
 30. The method of claim 27, wherein theinsulative cover comprises one of a tube or shell.
 31. The method ofclaim 27, wherein the second electrode comprises an array of tines. 32.The method of claim 27, wherein the second electrode comprises a singleconductive element.
 33. The method of claim 27, wherein the secondelectrode comprises a plurality of ring electrodes.
 34. The method ofclaim 27, wherein the longitudinal extent of the second electrode issubstantially equal to the deployed length of the coil-shaped electrode.35. The method of claim 27, wherein the target portion of tissuecomprises a tumor.
 36. The method of claim 27, wherein the targetportion of tissue comprises a uterine fibroid.
 37. A method of ablatingtissue, comprising: rotating a coil-shaped electrode to a first locationin a target portion of tissue; advancing a second electrode coaxiallycontained within the coil-shaped electrode to a second location in thetarget portion of tissue, the second location being distal to the firstlocation; applying current between the coil-shaped and second electrodesto ablate a first ablation portion of tissue; retracting an insulativecover proximally relative to the coil-shaped electrode; advancing thesecond electrode distally within the target tissue; and applying currentbetween the coil-shaped and second electrodes to ablate a secondablation portion of tissue.
 38. The method of claim 37, wherein thecoil-shaped electrode is contained within a tubular element and thecoil-shaped electrode rotates relative to the tubular element.
 39. Themethod of claim 37, wherein the coil-shaped electrode is secured to anelongate member and the coil-shaped electrode and elongate member arerotated together to distally advance the coil-shaped electrode.
 40. Themethod of claim 37 wherein the longitudinal extent of the secondelectrode is substantially equal to the deployed length of thecoil-shaped electrode.